Is bass stocking needed?

Largemouths can recover from catastrophic events, and wild fish do better than their expensive, hatchery reared brethren

In September 2004, Hurricane Ivan struck Alabama’s Gulf coast. Heavy rains caused a massive runoff of decompsing loads of organic matter flushed out of the watershed, resulting in a lot of oxygen-depleted water. Extensive fish kills took place throughout much of the Tensas-Mobile River Delta. Most of the dead fish were shad, but the oxygen depletion also killed largemouth bass. 

Assessments by biologists with the Alabama Division of Wildlife and Freshwater Fisheries documented a record-low 2004 year-class of largemouth bass. Assessments in 2007, the year the 2004 year-class would have recruited to the fishery, also documented a record-low abundance of catchable-size bass. Anglers campaigned for ADWFF to stock bass to restore the fishery.

Stock bayou bass

In 2009, ADWFF biologists initiated efforts to stock two bayous, one 30 acres and the other 170 acres, in the Delta to evaluate whether stocking would speed the recovery of the fishery. 

Adult largemouth bass were collected from the study areas from 2009 to 2011 and spawned at the Marion State Fish Hatchery. The progeny were reared on live forage to 5 to 6 inches and stocked at densities of 20 to 32 fish per acre in the springs of 2010, 2011 and 2012. The bass populations were intensively monitored to assess the effects of stocking.

Survival of age-1 fish — in their second year of growth —  that were stocked was similar to wild bass in the first year of evaluation but much lower during the second and third years of evaluation. The proportion of stocked fish in a year-class was highest shortly after stocking but steadily declined two and three years after stocking. The average wild fish was bigger than the average stocked fish.

Overall, the contribution of the stocked fish to the established, wild populations was low.

Lessons learned

The stocked fish made a minor contribution to the bass population after the fish kill, but the contribution decreased with time. The study, although designed to assess the effect of stocking on population recovery, also demonstrated the resilience of bass populations in the wild to drastic, short-term population reductions.

Apparently, sufficient healthy largemouth found refuges from the widespread oxygen depletions that caused the massive fish kill. With adequate habitat available, the surviving bass were able to repopulate the fishery; in this case, it required about six years.

Hurricanes are devastating events in many ways, and six years for recovery of a fishery is a long time, Could stocking have shortened this time period? Maybe a little, but not much.

A weak or missing year-class cannot be determined until the next spring. And documenting a weak or failed year-class rarely triggers immediate stocking. Every year, hatchery production is limited, and fish are produced for specific stocking needs. Stocking to fulfill an unexpected need means other, predetermined stocking needs must go unfilled.

Bigger fish

Large fish have better post-stocking survival than small fish. Stocking large fish, therefore, is more likely to accomplish the intent of stocking: increasing the population size. Producing larger bass for stocking takes time. It also is expensive and requires a lot of hatchery ponds to rear both the bass and the forage they need to grow. Hatchery managers have minimized the need for hatchery space by rearing young bass on prepared feeds similar to the way catfish are raised, but the survival of these pellet-fed fish in the wild may not be as good as fish reared on live forage.

Fish for stocking could have been available as soon as one year after the catastrophic event. With good survival, these fish would grow to catchable size in about three years. Yes, stocking may have accelerated the return of the fishery by one or two years. But the question remains: is stocking a good management strategy?

Cost effective?

The Mobile-Tensas Delta covers approximately 20,000 acres of aquatic habitat. Stocking this large an area, even at the lowest stocking rate used in the ADWFF study, would have required about 400,000 fish. Based on a survey of state fisheries agencies I compiled last year, the cost of production of large fingerling largemouth bass ranges from $0.50 to $2.80 per fish. Assuming hatchery production capacity is available, accelerating the return of the fishery by a few years would be very expensive. Stocking smaller fingerlings could be done sooner and at lower cost, but the survival of these fish is much less predictable.

Natural reproduction can restore a bass fishery at no cost after an environmental catastrophe if the habitat remains intact. However, a little patience is required.